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From: "rakdver at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/48702] [4.6/4.7 Regression] optimization regression with gcc-4.6 on x86_64-unknown-linux-gnu
Date: Thu, 21 Apr 2011 11:50:00 -0000	[thread overview]
Message-ID: <bug-48702-4-X64JdNqcJn@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-48702-4@http.gcc.gnu.org/bugzilla/>

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48702

--- Comment #6 from Zdenek Dvorak <rakdver at gcc dot gnu.org> 2011-04-21 11:49:36 UTC ---
I think we rely on the assumption that pointer arithmetics satisfies the
restrictions of C standard (i.e., that the pointer is within a single memory
object) on more places than just this one.  So, if the code produced by ivopts
is indeed

for (p = &a; p != &a - 3; --p)
  *(p + 3) = ...

this could potentially cause other problems other than with alias analysis.

But, I would expect the code from ivopts to be rather

for (p = &a; ...; p = (pointer) ((unsigned) p - 1)
  *((pointer) ((unsigned) p + 3)) = ...

Which should be a valid code.  Is that the case? If so, fixing alias analysis
would be the proper solution.


  parent reply	other threads:[~2011-04-21 11:50 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-04-20 14:12 [Bug rtl-optimization/48702] New: " mariah.lenox at gmail dot com
2011-04-20 14:29 ` [Bug rtl-optimization/48702] " rguenth at gcc dot gnu.org
2011-04-20 14:32 ` [Bug rtl-optimization/48702] [4.6 Regression] " rguenth at gcc dot gnu.org
2011-04-20 14:39 ` rguenth at gcc dot gnu.org
2011-04-20 15:08 ` [Bug rtl-optimization/48702] [4.6/4.7 " rguenth at gcc dot gnu.org
2011-04-21 10:48 ` rguenth at gcc dot gnu.org
2011-04-21 11:06 ` [Bug tree-optimization/48702] " rguenth at gcc dot gnu.org
2011-04-21 11:50 ` rakdver at gcc dot gnu.org [this message]
2011-04-21 12:32 ` rguenth at gcc dot gnu.org
2011-04-21 12:39 ` rguenth at gcc dot gnu.org
2011-04-21 12:58 ` rakdver at kam dot mff.cuni.cz
2011-04-21 13:06 ` rguenther at suse dot de
2011-04-21 13:35 ` rakdver at kam dot mff.cuni.cz
2011-04-21 16:22 ` xinliangli at gmail dot com
2011-05-12 12:10 ` rguenth at gcc dot gnu.org
2011-05-17 17:40 ` xinliangli at gmail dot com
2011-05-17 19:42 ` rakdver at kam dot mff.cuni.cz
2011-05-17 20:43 ` xinliangli at gmail dot com
2011-05-17 20:53 ` rakdver at kam dot mff.cuni.cz
2011-05-17 21:29 ` xinliangli at gmail dot com
2011-05-18  9:18 ` rguenther at suse dot de
2011-05-18 16:17 ` xinliangli at gmail dot com
2011-05-19  5:30 ` xinliangli at gmail dot com
2011-05-25 11:03 ` rguenth at gcc dot gnu.org
2011-05-25 11:06 ` rguenth at gcc dot gnu.org
2011-05-25 14:00 ` rguenth at gcc dot gnu.org
2011-05-26 10:05 ` rguenth at gcc dot gnu.org
2011-05-26 11:14 ` rguenth at gcc dot gnu.org
2011-05-26 13:03 ` rguenth at gcc dot gnu.org
2011-05-26 13:23 ` [Bug tree-optimization/48702] [4.6 " rguenth at gcc dot gnu.org
2011-06-06 10:14 ` rguenth at gcc dot gnu.org
2011-06-06 10:20 ` rguenth at gcc dot gnu.org

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